A Simulation Analysis And Experimental Study On Deep Penetration Laser Welding Of Aluminum Alloys

Aluminum alloys have such advantages as light weight, super inoxidizability, excellent electrical and thermal conductivity, and good mechanical properties under the low-temperature conditions. Hence, aluminum alloys have been widely used in automobile industry and aerospace industry. However, The weldabilities of aluminum alloys are quite poor because of their high thermal conductivity and some other physical properties, such welddefects as porosities and burning loss of some volatile elements (e.g. Mg and Zn) are apt to be produced in the welds in traditional welding processes (e.g. TIG and MIG), which prevent aluminum alloys from wide application. Laser welding is one of the effective methods to solve the above problems.Keyhole effect is the base of deep penetration laser beam welding. In order to study the keyhole effect during laser welding, the shape of the keyhole must be known first. However, because the keyhole is located inside the workpiece, it is difficult to observe directly in laser welding of metals. In this paper, the keyhole is experimentally observed by using a specially-designed composite workpiece, which is consisted of the following two parts: one is made from GG17 glass, the other one is made from aluminum alloys. From the transparent GG17 glass side, the keyhole can be directly observed during laser welding of aluminum alloys. The keyhole pictures have been taken by a high-speed camera. From the keyhole photographs, the shape and the size of keyholes have been measured, which can be used for further theoretical study. Experimental results showed that both the laser power and welding velocity used have great effects on the keyhole sizes and keyhole profiles.Based on the above experimentally-obtained keyhole photographs, a mathematical conductive model has been developed. Then, finite difference method and Matlab procedure have been used to solve the above mathematical model, and the temperature distribution during laser welding aluminum alloys and glass has been calculated. The results of numerical simulation indicated that both the laser power and welding velocity used have played great roles on the temperature distribution. Moreover, due to the obvious differences of the physical properties between aluminum alloys and glass, the temperature field during laser welding of them is far away from a symmetrical one. Same as the problem occurred in direct observation of the keyhole, the plasma plume and the high temperature emission inside the keyhole during laser welding metals are also difficult to observe and measure directly. In order to study the effect of the burning loss of such volatile elements as Magnesium and Zinc on the mechanical properties of the welds, the spectrum emitted from the keyhole has analyzed by using the same experimental setup as mentioned above. The results of spectral analyses showed that the burning loss of volatile elements during laser welding is closely related to such processing parameters as laser power and welding velocity. These results are very useful for choosing suitable processing parameters to reduce the ablation loss of Magnesium and Zinc in practice...